1. Field of the Invention
The invention relates to a ball screw.
2. Description of the Related Art
In a conventional ball screw with a nut, which has a thread groove formed in an inner peripheral face thereof, fitted on a screw shaft having a thread groove formed in the outer peripheral face thereof, and with a plurality of balls disposed in a ball passage formed by the thread groove of the screw shaft and the thread groove of the nut.
In the above-described ball screw, if the thread groove is formed along an entire length of the screw shaft, the nut may move beyond a stroke end and the balls may fall out from the end of the thread groove of the screw shaft, for example, when the ball screw is inspected, transported, or mounted on an actuator.
To address this problem, Japanese Patent Application Publication No. 2005-121216 (JP-A-2005-121216) describes the reduction of the thread groove width at the ends of the screw shaft through plastic deformation of screw head portions adjacent to the thread groove.
In the ball screw according to JP-A-2005-121216, the balls may be prevented from falling out from the region at the end of the thread groove having a reduced width, even if the thread groove is formed along the entire length of the screw shaft.
However, the plastic deformation of the screw head portions requires an additional major step. Furthermore, if the nut reaches a stroke end, the balls may become wedged in the region where the thread groove width has been reduced and thereby damaged.